Air data computer



March 8, 1966 R. w. ARMSTRONG 3,239,140

AIR DATA COMPUTER Filed April 27, 1962 2 Sheets-Sheet l ROBERT W.ARMSTRONG BY gym ATTORNEY.

March 8, 1966 R. w. ARMSTRONG AIR DATA COMPUTER 2 Sheets-Sheet 2 FiledApril 27, 1962 INVENTOR. ROBERT W. ARMSTRONG BY M ATTORNEY.

United States Patent O 3,239,140 AIR DATA COMPUTER Robert W. Armstrong,Mound, Minn., assignor to Honeywell Inc., a corporation of DelawareFiled Apr. 27, 1962, Ser. No. 191,685 7 Claims. (Cl. 235--200) Thisapplication is a continuation in part of a copending application, filedNovember 20, 1961, Serial Number 153,436 now abandoned, of the presentinventor and assigned to the assignee of the present invention.

This invention relates to control apparatus and more particularly to airdata computer apparatus utilizing novel static error correctionapparatus to convert signals indicative of indicated static pressure(PS1) to true static pressure (PS) and provide corrected outputs forthose aircraft components that rely on true static pressure for properindication.

It has long been known in the art that the static pressure received bythe sensing device or Pitot-static tube mounted on an aircraft becomesincorrect by an amount AP which varies as a function of aircraft speedin terms of Mach number M. A relationship may be expressed as:

where AP may be positive or negative depending on the relativemagnitures of Ps1 and PS. In the past a number of systems have beenproposed to provide a corrected static pressure source but all of thesesystems have had a number of disadvantages. Pneumatic systems have beenproposed which employ a pump or other pressure regulating devicecontrolled in accordance with the static error pressure AP to adjust thestatic pressure in such a manner that the pneumatic output thereof iscorrected static pressure Ps. These systems have had the majordisadvantage of slow response and for the most part are undesirable inthe present day high speed aircraft where fast response is critical.Other proposed systems include electrically rebalanced systems whereinan electrical signal is generated indicative of corrected staticpressure. Such electrical systems have had the major disadvantage thatthe present state of the art is incapable of manufacturing accurateenough components for these systems. A number of problems result such asundesirable quadrature signals, impedance matching and the like whichalso make such systems undesirable.

The present invention provides an output indicative of corrected staticpressure which is mechanical in nature and as such is not subjected tothe slow response of pneumatic systems nor to the undesirable feature ofelectric systems. Briey the present invention includes a pressuretransducer having indicated static pressure Psi as one input andproviding an output in the form of a shaft rotation in accordancetherewith. Amechanical static pressure error correcting device isprovided which receives as an input the shaft rotation produced by thetransducer device and also receives as a second input a shaft rotationwhich is characterized as a function of airspeed in terms of Machnumber. The mechanical static error correcting device operates uponthese two inputs to provide an output indicative of the static pressureerror AP which output is also in the form of a shaft rotation. This APsignal is mechanically coupled back to the transducing apparatus toadjust the apparatus in such a direction that the correction signal APis combined with the signal indicative of indicated static pressure Psiso that the output of the transducer becomes corrected static pressurePs. The output of the transducer which is now corrected static pressurePS may be used in the various portions of the aircraft instruments icewhere corrected static pressure is needed and no further correction isnecessary. The output of the static error corrector, as stated, is thecorrection signal AP and this in itself may be used to correct otherinstruments such as the differential pressure transducer.

A more complete understanding of the present invention will be obtainedupon examination of the following specication, claims and drawings inwhich:

FIGURE 1 is a schematic representation of the basic principle involvedin the static error correction mechamsm;

FIGURE 2 is a partly schematic and partly exploded view of the staticpressure transducer and static error correcting mechanism employing thepresent invention; and

FIGURE 3 is a block diagram of an air data cornputing system employingstatic error correction.

Referring now to FIGURE 1, a rotatable arm 10 is shown having alaterally extending ange 12 at one end thereof which contains a pivotaxis 14. The rotatable member 10 has a bearing surface 16 which extendsunder the ange portion 12 as shown by the dashed line 18.

Also shown in FIGURE 1 is a movable member 20 having a flange portion 22upon which is mounted a bearing member or roller 24. Roller 24 is causedto bear against the bearing surface 16 of member 10 and the pivot axis26 of roller 24 is such that it is the same distance from the bearingsurface 16 as the pivot axis 14 of member 10. By this arrangement it isseen that member 20 can be placed so that roller 24 is positioneddirectly under the ange portion 12 of member 10 so that axis 26 ofroller 24 would coincide with axis 14 of member 10.

Member 20 is caused by means not shown to move in a vertical directionunder the inuence of static pressure and under zero static pressureconditions axis 26 would coincide with axis 14. The verticaldisplacement of axis 26 from concidence with axis 14 will be controlledaccording to static pressure and in FIGURE 1 this distance has beenshown as the vertical line of a right triangle identified with referencenumeral PS.

Member 10 is caused to rotate as a function of aircraft speed in termsof Mach number. It is known that the static pressure error AP varieswith Mach number in a predetermined fashion and consequently the ratioAP/Ps is also a function of airspeed in terms of Mach number. Bycharacterized means, not shown in FIG- URE 1, member 1t) is caused torotate as a function of arc tangent AP/Ps and the amount of rotation hasbeen shown in FIGURE 1 as angle 0 which is the angle between thevertical side of the triangle Ps and the line joining axis 14 with axis26 which comprises the hypotenuse of the triangle shown in FIGURE 1.

The amount of horizontal movement of axis 26 from the zero staticpressure condition has been shown in FIG- URE 1 as the distance of thehorizontal portion of the triangle identified by reference numeral X. Itis clear from FIGURE 1 and the triangle that X :Ps tangent 6 and since,as previously stated, 0 is caused to be a function of arc tangent AP/Ps,

X =KPs tangent (are tangent Ps AP X- KPS( Ps static error signal AP andmeans are provided not shown in FIGURE l to measure this horizontaldisplacement `and convert it into the AP signal used for the remainderof the system.

FIGURE 2 shows a practical embodiment of the present invention includingin the lower portion the static pressure transducer identified byreference numeral and in the upper portion the static error correctionmechanism identified by reference numeral 52.

The static pressure transducer comprises a Z-shaped member which isfixed to the container (not shown) which houses the transducermechanism. Zshaped member 55 has two oppositely directed flanges 57 and58 at either end thereof which flanges have connected thereto a pair ofpressure sensitive devices or bellows 61 and 62 respectively. Bellows 61and 62 are both evacuated in the static pressure transducer 50 while theinterior of the container is supplied with the indicated static pressurePs1 provided from the Pitot-static probe on the aircraft. Thus as theindicated static pressure changes bellows 61 and 62 will each contact orexpand. Since bellows 61 and 62 are oppositely directed, they produceforces with changes in indicated static pressure in opposite directions.Bellows 61 and 62 each have a force applying linkage shown in FIGURE 2as bars 66 and 67 respectively. Bars 66 and 67 `are connected onopposite sides of a generally O-shaped yoke 70. Yoke 70 is mounted onthe Z-shaped member 55 by a quadrilever type spring 72 which is fastenedlto the Z-shaped member 55 at the center and which extends in oppositedirections to the yoke 70 where it is fastened as at 75 and 76respectively. This quadrilever type spring 72 provides a spring biasedpivot for the yoke 70 and since bellows 61 and 62 apply forces varyingwith PS1 to yoke member 70 in opposite directions, changes in Psiproduce a torque on yoke member 70 which turns yoke member 70 withrespect to -the Z member 55 by an amount depending upon the stiffness ofthe transducer system spring rate and the amount of change of Ps1.

Yoke member 70 has a lateral extension 80 which is in the form of amagnetic armature cooperating with an E-shaped transformer S3 which isconnected Ato the container housing the transducer 50 by means notshown. It is seen however that rotation of yoke 70 causes displacementof armature 80 with respect to E transformer 83 whenever the indicatedstatic pressure PS1 changes. This displacement of the armature 80 withrespect to the E transformer 83 produces a signal on wires 8S, 86 and 87which lead to a motor shown generally las 90. Thus any change inindicated static pressure Ps1 will cause motor 90 to operate in a firstor second direction depending upon whether Psi has increased ordecreased. Of course, other type pickoff means may be employed in placeof E transformer 83 and if necessary an amplifier may be used betweenthe pickoff and the motor 90.

Motor 90 has an output shown by dashed line 95 which is shown in FIGURE2 terminating at reference numeral A. The dashed line connection 95 isconnected by means not shown in FIGURE 2 to a corresponding referencenumeral A', shown in the upper portion of `the drawing, which isconnected by mechanical connection shown as dashed line 96 to a gearsector 98 which forms a portion of a torsion tube 100. As will bedescribed with regard to FIGURE 3, various apparatus may be includedbetween the reference numerals A and A such as gear trains and cams butare not shown in FIGURE 2 for purposes of clarity. Torsion tube 100 hasa clamp 102 at the upper end thereof which clamps a torsion bar 104.Torsion bar 104 is shown generally rectangular in cross section andextends down through the torsion tube 161) and down through the centerof the quadrilever spring 72 and is clamped to the yoke member '71B atthe bottom portion thereof by a clamp 108. It is seen that rotation ofmotor 90 operating through mechanical connections 95 and 96 will causerotation of gear sector 98 and torsion tube 100 -to apply a torque tothe torsion bar 104 which in turn transmits this torque to the yokemember 70. Rotation of yoke member 70 occasioned by a change inindicated static pressure Psi will thus cause movement of armature withrespect to a transformer 83 and drive motor in such a direction that therotation of torsion tube and torsion bar 104 applies an oppositelydirectly torque to the yoke member 70 to accomplish rebalance of thesystem. That is to say, as soon as yoke member 7l) rotates under theinuence of a change in indicated static pressure Ps1 an oppositelydirected torque is applied by means of torsion bar 104 to yoke member'79 to return it to its original state of equilibrium at which timemotor 9i) stops and the position thereof would be indicative of the newindicated static pressure Psi.

Also connected to the output of motor 90 is a mechanical connectionshown as dashed line 112 which operates `to turn a gear 115 in thestatic error correction mechanism 52. Gear 115 cooperates with a rack116 which is part of a member 117 in the static error correctormechanism 52. Member 117 is provided with guide means such as a trough121i in which a pair of rollers 123 and 124 operate. Rollers 123 and 124are connected to the frame or casing (not shown) housing the staticerror correction mechanism 52. Member 117 also has a lateral extensionin `the form of a flat plate which extends to the left in FIGURE 2 andwhich has a vertically extending abutment 133 at the remote end thereof.Vertically extending abutment 133 is also provided with guide means suchas a trough 135 in which members such as roller 137 operate. Roller 137is likewise connected to the frame or casing (not shown) housing thestatic error correction mechanism 52. Rollers 123, 124 and 137 operateto guide member 117 and the lateral extension 130 in a directiongenerally into and out of the plane of the drawing of FIGURE 2. As seen,energization of motor 90 will cause rotation of gear 115 which will inturn cause motion of member 117 as guide by rollers 123, 124 and 137.

Member 117 carries a pair of rollers or guide members 141) and 141 andalso carries on the vertically extending abutment 133 a pair of rollersor guide members 144 and 145. Rollers 141), 141, 144 and 145 on member117 cooperate with a generally T-shaped member 150 and operate to guidemember in a direction perpendicular to the motion of member 117. That isto say, T-shaped member 150 is able to move in a direction substantiallyparallel to the plane of the drawing of FIGURE 2.

Member 150 has a lateral extension 153 which in turn carries a guidemember such as a roller thereon. Roller 155 is positioned so as to bearon a surface 160 of a rotatable member 162.

Rotatable member 162 is shown in FIGURE 2 as formed like an open box`through which member 150 extends in such a manner that roller 155 cancooperate with the surface 160. Member 162 also has a laterallyextending portion 165 which carries a pivot 166. Pivot 166 is positionedon extension 165 at a distance from surface 160, which extends underextension 165, equal to the distance from the pivot of roller 155 to thesurface 160. This enables roller 155 to occupy a position whereby itspivot is directly under pivot 166. Pivot 166 is connected by bearingmeans (not shown) to the frame or casing housing the static errorcorrection mechanism 52 so that it is free to rotate with respectthereto. Connected to the upper portion of pivot 166 is a follower arm172 which extends to a cam 174 and which has a roller or follower means175 cooperating with the surface of cam 174. Cam 174 in turn has a shaftconnected thereto which is caused to rotate by means not shown in FIGURE2 as a function of airspeed in terms of Mach number as indicated by thearrow and the designation M in FIGURE 2.

In the apparatus thus far described it is seen that rotation of shaft180 will cause rotation of cam 174 and will thus cause movement offollower arm 172 which operating through pivot 166 will cause rotatablemember 162 to rotate. This rotation will be accompanied by movement ofthe roller 155 to the left or to the right in FIG- URE 2 depending uponthe direction of rotation of member 162. Likewise it is seen thatrotation of shaft 112 connected to motor 90 will cause rotation of gear115 and thus cause movement of member 117 generally into or out of theplane of the drawing of FIGURE 2. This movement of member 117 will beaccompanied by movement of member 150 to the right or to the left sinceroller 155 is caused to bear against surface 160.

As explained with regard to FIGURE l, motion of member 150 to the leftor to the right is a product of the amount of movement of member 117 andthe tangent of the angle through which rotatable member 162 has rotated.As stated, the motion of member 117 is proportional to static pressureas provided by the motor 90 and rotation of member 162 is proportionalto a desired function of Mach number. Cam 174 is so characterized thatrotation of member 162 is proportional to the arc tangent of the ratioAP/Ps -which ratio is known to be a predetermined function of aircraftspeed in terms of Mach number. Thus, motion of member 150 to the leftand to the right is indicative of the correction factor AP since themechanism operates to multiply the ratio AP/PSXPS.

This motion to the right or to the left indicative of AP is transmittedfrom member 150 by means of a T-shaped extension 190 at the left endthereof which cooperates with a guide member of roller 192 connected toa rack 194. Thus motion of member 150 will be accompanied by motion ofrack 194 and this motion 4is transmitted to a gear 196 which is mountedon a shaft 198. It is seen that rotation of shaft 198 is alsoproportional to the static error correction AP. Spring means shown asarrow 200 operate on rack 194 to force roller 192 against the T-shapedsurface 190 and thus push member 150 and roller 155 against the surface160 of rotatable member 162. Spring 200 therefore holds the mechanism inan engaged position with the various rollers and surfaces biased towardseach other.

As stated shaft 198 rotates in accordance with the static errorcorrection AP and this rotation is imparted to a gear sector 204connected at the l-ower end thereof.

Gear sector 204 cooperates with a gear sector 208 which forms a part ofa member 210. Member 210 has rst and second elongated extensions 212 and214 respectively which are attached to a pair of cantilever springmembers 216 and 218 as shown by dashed lines 220 and 222. Springs 216and 218 are fastened to the lower portion of yoke member 70 on oppositesides and spaced from clamp 108 by means of a pair of extensions such asshown at 228. It is seen that as gear sector 204 rotates member 210 willrotate which will in turn apply a torque to yoke member 70 throughsprings 216 and 218. Since the rotation of gear sector 204 isproportional to that `of shaft 198 which in turn is proportional to thestatic error correction quantity AP, the correcting force applied frommember 210 through springs 216 and 218 to yoke 70 is proportional to thestatic error correction AP. This correction torque on yoke member 70causes movement thereof in a direction which when taken together withthe torque applied from the indicated static pressure Psi provides thenecessary correction and the resultant movement of yoke member 70 isproportional to corrected static pressure Ps. Stated differently, themechanism shown in the force transducer 50 applies a correcting force APwhich is algebraically summed with the indicated static pressure forcePS1 to provide an output Ps which as mentioned is related to correctedstatic pressure Ps by the equation PSi-PS=AP. Thus it is seen that thepressure transducer 50 has an output proportional to corrected staticpressure PS which output may be utilized in the aircraft for thoseindications where corrected static pressure is necessary.

Also shown in FIGURE 2 is a member 250 which has a pair of upwardlyextending cylindrical portions 252 and 253. Portions 252 and 253 ofmember 250 when the unit is assembled are attached to the Z-shapedmember 55 at holes 260 and 261 respectively as shown by dashed lines 264and 265. Member 250 has a bearing connection with `member 210 at theportion between them shown by arrow 270 so that member 210 is free torotate with respect to member 250.

Also shown in FIGURE 2 is a force applying device 275 attached to theyoke member 70 at point 277. Member 275 carries a temperature sensitiveelement 279 which operates to apply a force to the yoke member 70 inaccordance with temperature and thereby provide the transducer 50 withtemperature compensation.

Also shown in FIGURE 2 is a transducer 300 identitied with the letterqc. Transducer 300 is substantially identical in structure to staticpre-ssure transducer 50 herein described and will not be itselfdescribed in detail. The only difference between the qc transducer 300and the static pressure transducer 50 is that the qc transducer producesan output proportional to the difference between total pressure PT andstatic pressure PS. This difference is dened as qc and requires that thetransducer have two inputs PT as shown by conduit 303 and Ps1 as shownby conduit 304. The interior of transducer 300 will be the same as theinterior of the static pressure transducer 50 herein described exceptthat the bellows 61 and 62 which were described as evacuated in thestatic pressure transducer 50 will have static pressure applied to theirinteriors and total pressure PT in the case will be applied to theirexteriors. Therefore in the q,3 transducer 300 motion of the yoke membercorresponding to member 70 will be in accordance with the differencebetween total pressure PT and static pressure Ps. Transducer 300 has aninput correcting for the static error AP by means of a shaft 308 whichcorresponds to the shaft 198 for the static pressure transducer 50.Shaft 308 is connected to a gear 310 which is in turn connected to agear 312 mounted on the shaft 198. Therefore as the rack member 194moves in accordance with static error correction AP, gear 312, gear 310and shaft 308 will rotate accordingly. By a mechanism similar to thatshown in describing the static pressure transducer 50, this correctionfactor AP will be applied to the qc transducer so that its output isindicative of the difference between total pressure PT and correctedstatic pressure Ps.

Referring now to FIGURE 3, which shows in schematic diagram form oneembodiment of an air data cornputer incorporating the static e-rrorcorrection, a Ps transducer 50, which may be the same as that apparatusshown in FIGURE 2, is shown having an input conduit 400 which providesthe transducer with the pressure Psi derived from the indicated staticpressure source on the aircraft. A mechanical input shown as dash line402 is shown connected to transducer 50 to :supply the transducer withthe correction signal AP. Mechanical connection 402 is shown connectedby a second mechanical connection 405 to the static error corrector 52which may be the same as that shown in FIGURE 2. Mechanical connections402 and 405 may comprise the apparatus including roller 192, rack 194,gear 196 and shaft 198 of FIGURE 2.

Static pressure transducer 50 provides an electrical output whenever achange in true static pressure Ps causes unbalance of transducer 50.This output is shown in FIGURE 3 as emerging on conductor 407 and beingfed to a summing network 409 which is in turn connected by a conductor411 to an amplifier 412. The output of amplier 412 drives motor by meansof a connection 415. Motor 90 is FIGURE 3 is the equivalent of motor 90in FIGURE 2 and the conductor 407, summing network 409, conductor 411,amplifier 412 and connection 415 comprise apparatus placed between Etransformer 83 and motor 90 which in FIGURE 2 was shown merely asconductors 85, 86 and 87.

Rate feedback is provided in FIGURE 3 by means of a velocity generator420 connected to motor 9) by a mechanical connection shown as dash line421. The output of velocity generator 428 is fed to a resistor 423 by aconductor 424. Resistor 423 includes a movable wiper 425 which isconnected back to the summing network 409 to provide the desired ratefeedback.

The mechanical motion of motor 90 is caused to rebalance the Istransducer t) in the following manner. A mechanical connection 427 isplaced between motor 90 and a gear train 429. Gear train 429 has a rstoutput connection 431 leading to a second gear train 432. Gear train 432has mechanical connection 433 leading to a characterized cam shown inFIGURE 3 as a tape cam 435. Cam 435 is so characterized that it convertsmotion indicative of a first condition to a Imotion indicative of thelog of the first condition or vice-versa. Specifically this cam is socharacterized as to concert log of Ps to PS. Thus if a first portion 437of cam 435 turns as the log of Ps a Isecond portion 438 of cam 435 willturn as Ps. Cam 435 has a mechanical connection shown as dash line 440connected to a second mechanical connection shown as dash line 442 to agear train 443 and from there by a mechanical connection `shown as dashline 444 to the Ps transducer 58 to accomplish rebalance. Connection 442is also shown providing an input to the static error correctionmechanism 52. The mechanical connections above described between motor90 and Ps transducer 50 including elements 427 through 444 may compriseapparatus between A and A in FIGURE 2. Likewise the connections frommotor 90 to the static error corrector 52 including elements 427 through442 may correspond to the mechanical connection 112 in FIGURE 2.

Because cam 435 is characterized to convert log Ps to Ps, motor 90 iscaused to turn as a function of log PS. Gear trains 429 and 432 operateto reduce the numbe-r of turns of motor 90 to a value compatible withthe limited amount of rotation available with cam 435. Since motor 90operates as a function of log Ps, mechanical connections 427, 431 and433 also operates as functions of log Ps. However, mechanicalconnections 440, 442 and 444 operate as a function of Ps itself sincethey are on the far side of cam 435. Therefore, as described inconnection with FIGURE 2, an input on mechanical connection 442indicative of Ps is presented to the static error corrector 52 and arebalance signal indicative of Ps is presented to transducer 5t) bymechanical connection 444.

It has been found that the stability of the above described servo loopchanges as a function of static pressure so as to tend to be overdampedat low pressures. To compensate for this change in mechanical gain, amechanical connection shown as dash line 450 is connected between geartrain 432 and the wiper 425 associated with the rate feedback networkabove described. Mechanical connection 450 turns as a function of log Psas above described and operates to position wiper 425 so that variousamounts of rate feedback damping are provided depending upon themagnitude of the static pressure. By providing more or less ratefeedback damping signal in accordance with the magnitude of staticpressure, servo loop damping compensation for the change of stability inthe servo loop with change of static pressure is accomplished thuspreserving optimum frequency response.

Also shown in FIGURE 3 is the qc transducer 388 having a Psi input fedthereto by means of conduit 384 and a PT input fed thereto by means ofconduit 303. A mechanical connection from the static error corrector 52is provided for the qc transducer 308 as shown by dash lines 460 and405. The mechanical connections 405 and 460 may comprise the roller 192,rack 194, gears 196, 312 and 310 and the shaft 388 of FIGURE 2.

An electrical output from the qC transducer is provided on the conductor462 which is shown connected to a summing network 463 and then by aconductor 464 to an amplifier 465. Amplifier 465 is connected to a motor467 by a connection 468. Rate feedback for this motor is provided bymeans of a velocity generator 469 connected to motor 467 by a connectionshown as dash line 470. The output of velocity generator 469 ispresented to a resistor 472 by a conductor 473. Resistor 472 has a wiper475 connected back to the summing network 463 to provide the requisiterate feedback. The output of motor 467 is shown as a dash line 480connected to a gear train 482.

Rebalance of the qc transducer is provided by a connection shown as dashline 483 from gear train 482 to a second gear train 485. Gear train 485is connected to a characterized -cam 487 by a connection shown as dashline 488. Cam 487 may be a tape cam like cam 435 and has a first portion489 and a second portion 490. The characterization of cam 487 is suchthat as cam 489 rotates as a function of log qc portion 490 will rotateas a function of qc. Cam 487 is connected to q,2 transducer 380 bymechanical connection shown as dash line 492, a gear train 493 and amechanical connection shown as dash line 495. Because of thecharacterization of cam 487, motor 467, mechanical connection 480,mechanical connection 483 and mechanical connection 488 move asfunctions of log qc whereas mechanical connections 492 and 495 move asfunctions of qc. Connection 495 to qC transducer 308 provides rebalancein much the same fashion as was described with regard to the Pstransducer 50 in FIGURE 2. Gear trains 482, 485 and 493 are used forpurposes of converting the amounts of rotation of the shafts to smalleror larger quantities as desired.

As with the Ps servo loop, the qc servo loop also changes gain inaccordance with changes of qc. A similar means of compensating for thischange of gain is shown in FIGURE 3 as a mechanical connection shown asdash line 496 connected between gear train 485 and wiper 475 of resistor472. As qc changes, mechanical connection 496 will move wiper 475 toprovide more or less rate feedback and to compensate for the change ingain.

As previously stated the output of motor 98 is operating at the functionof log Is and the output of motor 467 is operating as a function of logqc. Gear train 429 has a connection shown as dash line 501 connected toa differential 503. This connection provides an input to thedifferential 503 which is a function of log Ps. Gear train 482 has amechanical connection shown as dash line S05 connected -to differentialmeans, often termed a summing means 503. This provides an input todifferential 503 which is a function of log qc. The output of thedifferential is the algebraic difference between the two inputs and thisoutput is shown as dash line 510 in FIGURE 3. The signal on the outputconnection 510 may be expressed Since qczPT-Ps Equation 1 becomes Logqo-log P=Lo (l) PT Ps has long been recognized as a function of airspeed in terms of Mach number and is usually written as R-l where R isdefined as PT/PS. The motion of mechanical connection 510 is therefore afunction of log (R-l) which in turn is a function of Mach number.Mechanical connection 510 is shown connected to a gear train 512 andthen by a mechanical connection shown as dash line 513 to a cam 515. Cam515 is shown as a tape cam but unlike cams 435 and 487 is characterizedto convert the function log (R-l) to a function of Mach number M. Thatis to say, as a first portion 517 of cam 515 rotates as a function oflog (R-1), a second portion 519 of cam 515 moves as a function of Machnumber M. Almechanical connection shown as dash line 520 connected tocam 515 therefore rotates as a function of Mach number M. Connected tomechanical connection 520 is another mechanical connection shown as dashline 525 which is shown leading to a cam and follower arrangementsimilar to that shown in FIGURE 2 as cam 174 and follower arm 172. Thepurpose of this cam arrangement is to provide an output indicative ofthe quantity iP/Ps which, as previously explained, is a function of Machnumber. This motion is presented to the static error corrector 52 bymeans of a mechanical connection shown as dash line 527. Mechanicalconnection 525 may be equivalent to the shaft 180 shown in FIGURE 2while mechanical connection 527 may be equivalent to the pivot 166 inFIGu URE 2. It should be remembered at this point that log (R-l) is initself a function of Mach number and if desired connection 525 could beconnected to mechanical connection 510 rather than mechanicalconnec-tion 520 providing cam arrangement 174, 172 were characterized soas to convert log (R-l) to a function of AP/Ps.

As shown with regard to FIGURE 2 the static error correction mechanism52 operating on an input of Ps and an input of AP/Ps produces therequired correction signal AP which is shown in FIGURE 3 as emerging onmechanical connection 485 and is presented to the Ps transducer 50 andthe qc transducer 300 by mechanical connections 402 and 460 respectivelyto provide the requisite correction for static pressure error.

In order to produce a number of outputs necessary for aircraft operationthe air data computer as shown in FIGURE 3 has a variety of connectionsto various portions within the computer each operable to produce adesirable output. As examples of the kinds of outputs frequently desiredin air data computers FIGURE 3 shows 1l terminals numbered 550 through560. Terminal S50 is shown producing an output d Log Ps dT or rate ofchange of log Ps. This output is a known function of rate of change ofaltitude lip. Rate of change of log Ps is easily derived in the circuitof FIGURE 3 by a connection shown as conductor 562 connected to theoutput conductor 424 of velocity generator 420. As previously statedmotor 90 is turning as a function of log Ps and therefore velocitygenerator 420 produces an output indicative of rate of change of log Ps.Standard characterized means may be employed to convert the signal d LogPs dT to lip.

Terminal 551 is shown having an output of log Ps. This output is derivedby a mechanical connection shown as dash line 564 connected to amechanical connection 450 which as previously mentioned moves as afunction of log Ps. Of course, mechanical connection 564 could beconnected elsewhere in this system and still obtain a signal indicativeof log Ps. For example an output from gear train 429, mechanicalconnection 431 or mechanical connection 433 could be connected tomechanical connection 564 since each of these connections is moving as afunction of log Ps.

Terminal 552 is shown producing an output Ps. This is derived in FIGURE3 by mechanical connection shown as dash line 556 connected tomechanical connection 442 which as previously mentioned moves as afunction of Ps. `As before, mechanical connection 566 could be connectedelsewhere in the circuit and still obtain a Ps output. For exampleconnection 566 could be connected to connection 444 or gear train 443 aseasily.

Terminal 553 is shown producing an output A log Ps or change of log Psfrom some predetermined value. The change of log Ps output is a knownfunction of change of altitude hp and may be used as an altitude holdsignal for the aircrafts autopilot. This altitude hold signal is derivedfrom a connection shown as dash line 568 which is connected to oneportion of a clutch 569, the other portion of which 570 is connected togear train 429 by a connection shown as dash line 571. Clutch 570 may beoperated electromagnetically by means of a coil 572. As previouslystated the outputs from gear train 429 operate as functions of log Psand so connection 571 also moves as a function of log Ps. Since log Psis a function of altitude h, when altitude hold is desired the coil 572may be energized by the pilot thereby engaging clutch members 569 and570. From the time of engagement of clutch, a signal is presented tooutput terminal 553 which will show change of log Ps from that whichexisted at the time of engagement. This change of log Ps may be usedthereafter to control the autopilot and hold the aircraft at thepredetermined desired altitude. Clutch member 569 may be connected to arecentering spring not shown to bring clutch member 569 back to itsinitial position when the clutch is again deenergized.

Output terminal 554 is shown producing an output indicative of altitudehp. This is derived from a mechanical connection shown as dash line 575connected to cam 577. Cam 577 is connected by a mechanical connectionshown as dash line 578 to the mechanical connection 433 which aspreviously stated is moving as a function of log Ps. Cam 577 is socharacterized as to convert log Ps to altitude hp.

Output terminal 555 is shown producing an output of indicated air speedVc. This output is obtained by a mechanical connection shown as dashline 580 connected to a cam S82. Cam 582 is connected by a mehanicalconnection shown as dash line 583 to mechanical connection 488. Aspreviously stated mechanical connection 488 is moving as a function oflog qc and hence connection 583 moves as a function of log qc. Cam 582is so characterized as to convert log qc to indicated air speed Vc.

Output terminal 556 is shown producing a Mach number output M. This isderived from a mechanical connection shown as dash line 585 connected tomechanical connection 520 which as previously described moves as afunction of the Mach number.

Output terminal 557 is shown producing an output indicative of change oflog (R-l). This in turn is a function of change in Mach number and maybe used t0 produce a signal for the autopilot to provide a Mach holdfunction. The output of terminal 557 is derived from a mechanicalconnection shown as dash line 588 which is shown connected to oneportion of a clutch 589, the other portion 590 of which is connected bya mechanical connection shown as dash line 591 to mechanical connection510. As previously stated mechanical connection 510 moves as a functionof log (R-1) so that mechanical connection 591 similarly moves. Also aspreviously stated log (R1) is a function of Mach number. Clutch members589 and 590 are engaged by a coil 592 so that when it is desired to holdMach, the pilot may engage members 589 and 590 after which mechanicalconnection 588 moves with mechanical connection 591. A signal is thusprovided indicative of change of Mach number from the value existing atthe time of engagement. This signal may be sent to the autopilot toprovide the desired Mach hold function. As with clutch 569, 570, clutch589, 590 may be recentered by means of a spring not shown so that whenthe clutch is deenergized member 589 will return to its originalposition.

Output terminal 558 is shown producing a signal indicative of qc. Thissignal is obtained from a mechanical connection shown as dash line 593connected to mechanical connection 492. As previously stated connection492 moves as a function of qc so that shaft 593 moves likewise.

Output terminal 559 is shown producing a signal indicative of log qc.This signal is derived from amechanical connection shown as dash lineS95 connected to the mechanical connection 496. As previously statedconnection 496 moves as a function of log qc and hence connection 595does likewise.

Output 560 is shown producing a signal indicative of d Log (R-l) dT orrate of change of log (R-l). Rate of change of log (R-l) is proportionalto rate of change of Mach and hence the signal at output 560 may be usedto be indicative of Mach rate. This signal is derived from a conductor600 shown connected to a summing apparatus 602 which may be a standardsumming amplifier. Summing apparatus 602 is connected to the output ofvelocity generator 469 by a conductor 604 and is connected to the outputof velocity generator 420 by conductor 562 and a conductor 606. A signalfrom velocity generator 469 is indicative of a rate of change of qcwhereas the signal from velocity generator 420 is indicative of rate ofchange of Ps. When combined in summing network 602 an output is obtainedwhich is indicative of rate of change of qc/Ps which as previouslydefined is a function of rate of change of Mach.

As stated previously with regard to the outputs log Ps and Ps theconnections leading t0 the other 4outputs can be connected elsewhere inthe circuit. For example, qc output on 558 could be connected bymechanical connection 593 to connection 495 rather than 492 and the logqc output on terminal 559 could be connected to mechanical connections480, 483 or 488 rather than connection 496. I therefore do not intend tobe limited to the specific connections shown in FIGURE 3 since oneskilled in the art could place the connections to other appropriateplaces to take best advantage of gear train scale factors.

The various shaft outputs 550 through 569 in FIGURE 3 may be connectedto data transmitting devices such as synchros or potentiometers tosupply signals to indicators and autopilot components in a standardstraight forward manner bearing in mind that several of the outputswould necessarily require some characterization before final usage. Forexample with regard to the output at terminal 550 which was stated asvarying with the rate of change of log Ps, when it is desired to providean indication or an autopilot signal indicative of altitude rate thissignal must be characterized to convert log Ps to hp. Likewise thealtitude hold and Mach Ihold signals appearing on terminals 553 and 557are only functions of these conditions and apparatus such ascharacterized potentiometers may be necessary to change Alog PS, to Ahpand Alog (R-l) to AM. Such characterization is straight forward state ofthe art procedure and will not be described in detail here.

It is thus seen that apparatus has been provided which produces amechanical output indicative of corrected static pressure Ps and that anair data computer incorporating this apparatus has been provided whichsupplies a number of useful outputs to be utilized by the aircraft.Also, since static error correction is accomplished at the pressuretransducers, all outputs are compensated for the error in indicatedstatic pressure. It is further seen that the inherent disadvantages inelectrical and pneumatic systems have been overcome by means of thisnovel structure and that the apparatus provided is simple and easilymanufactured and assembled. Furthermore it is noted that the variouspressure transducers identified as the static pressure transducer qchave identically the same form and may be constructed in the same mannerthereby reducing manufacturing costs. Likewise the static errorcorrection mechanism provides an output which may be utilized by both ofthe pressure transducers rather than having a separate corrector foreach transducer. This feature again simplifies the manufacturingprocess. Another avantage is seen in the transducer itself wherein theelements are so arranged around the pivot axis that symmetry isachieved. This is to say the Z-shaped member and the bellows arearranged on opposite sides of the pivot axis so as to minimize anyvibration and acceleration effects that might be produced in the systemwhen it is mounted in an aircraft.

Finally it should be noted that lmany modifications may be made to thestructure herein described without departing from the spirit of theinvention. For example, it is within the skill of one in the art tomodify the various shapes and connections herein in many obvious ways.

I therefore do not intend to be limited by the specific elementsdescribed in connection with the preferred embodiment but intend only tobe limited by the following claims.

What is claimed is:

ll. Air data computing apparatus comprising in combination:

first pressure transducing means having a first input connected to asource of indicated static pressure Ps1, a second input connected to asource of pressure correction signal AP and an output Ps; first motivemeans connected to said first pressure transducing means and operable bythe output thereof to produce `a mechanical motion indicative of log Ps;

first rebalance means including means characterized to convertmechanical motion indicative of log Ps to mechanical motion indicativeof Ps;

means connecting said first rebalance means to said first motive meansand to said first pressure transducing means to provide rebalance ofsaid first pressure transducing means;

second pressure transducing means having a first input connected to thesource of Ps1, having a second input connected to a source of totalpressure PT, having a third input connected to the source of AP and anoutput;

second motive means connected to said second pressure transducing meansand operable -by the output thereof to produce a mechanical motionindicative of 10g qc;

second rebalance means including means characterized to convertmechanical motion indicative of log qc to mechanical motion indicativeof qc;

means connecting said second rebalance means to said second motive meansand to said second pressure transducing means to provide rebalance ofsaid second pressure transducing means; mechanical difference meansconnected to said first motive means and to said second motive means andoperable to provide a mechanical output motion indicative of thedifference between log Ps and log qc;

further characterized means connected to said mechanical differencemeans and operable to convert the mechanical output motion thereof to asignal indicative of Mach number M;

means connected to said further characterized means and to the source ofAP signal to provide a signal indicative of the ratio AP/Ps to thesource of AP signal;

and means connected to said first rebalance means and to the source ofAP signal to provide a signal indicative of Ps, said source of AP signaloperating to multiply the AP/Ps, signal and the Ps signal so as toproduce a signal indicative of AP.

2. An air data computer comprising, in combination:

a source of indicated static pressure Psi;

a source of total pressure PT;

static error correction means providing an ouput signal AP indicative ofthe error between PS1 and corrected static pressure Ps;

first pressure transducing means having a first input connected to saidsource of PS1, having a second input connected to said static errorcorrection means to receive the signal AP, having a rebalance input andoperable upon unbalance of the signals at the various inputs to producean output sign-al;

second pressure transducing means having a first input connected to saidsource of Ps1, having a second input connected to said source of PT,having a rebalance input and operable upon unbalance of the signals atthe various inputs to produce an output signal;

first rebalance means including characterized means operable to convertsignals indicative of log Ps to signals indicative of Ps and includingmotive means connected to the characterized means;

'( means connecting'the motive means of said first rebalance means tosaid first pressure transducing means to receive the output signaltherefrom;

means connecting the characterized means of said first rebalance meansto the rebalance input of said first pressure transducing means, themotive means of said first rebalance means operable in accordance withthe output signal fromsaid first pressure transducing and with thecharacterized means to produce a signal indicative of log Ps, thecharacterized means of said first rebalance means operable to presentthe signal indicative of Ps to said first pressure transducing means torebalance said first pressure transducing means;

second rebalance means including characterized means operable to convertsignals indicative of log qc to signals indicative of qn and includingmotive means connected to the characterized means;

means connecting the motive means of said Second rebalance means to saidsecond pressure transducer to receive the output signal indicative ofchange f qc;

means connecting the characterized means of said second rebalance meansto the rebalance input of said second pressure tr-ansducing means, themotive means of said second rebalance means operable in accordance withan output signal from said first pressure transducing means to produce asignal indicative of log qc, the characterized means of said secondrebalance means operable to convert the signal indicative of log qc to asignal indicative of qc and to present the signal indicative of qc tosaid second pressure transducing means to rebalance said second presuretransducing means;

' computer means having a first input connected to said first rebalancemeans to receive a signal indicative of log Ps, having a second inputconnected to said second rebalance means to receive a signal indicativeof log qfl and operable to produce an output signal indicative of Machnumber M;

conversion means connected to said computer means to receive the signalindicative of M and to produce an output signal indicative of the ratioAP/Ps;

and means connecting said static error correction means to said firstrebalance means and to said conversion means to receive signalsindicative of Ps and AP/Ps, said static error correction means operatingto multiply Ps and AP/Ps to produce an output signal indicative of AP.

3. In an air data computer:

a first member;

means mounting said first member for movement from a predeterminedposition in accordance with a plurality of forces;

means applying a first of the plurality of forces to said first memberin accordance with indicated static pressure Ps1;

means applying a second of the plurality of forces to said first memberin accordance with static pressure error AP, said first member movingfrom the predetermined position in accordance with corrected staticpressure Ps;

first rebalance means connected to said first member and operable inaccordance with movement of said first member from the predeterminedposition to apply a rebalance force to return said first member to thepredetermined position;

a second member;

means mounting said second member for movement from a predeterminedposition in accordance with a plurality of forces;

means applying a first of the plurality of forces to said second memberin accordance with Psi;

means applying a second of the plurality of forces to said member inaccordance with total pressure PT;

means applying a third of the plurality of forces to said second memberin accordance with AP, said second member moving from the predeterminedposition in accordance with pressure differential (PT-Ps);

second rebalance means connected to said second member and operable inaccordance with movement of said second member from the predeterminedposition to apply a rebalance force to return said second member to thepredetermined position;

computer means connected to said first and said second rebalance meansto receive signals indicative of functions of PS and (PT-Ps) therefromand operable to produce an output signal which is afunction of Machnumber M;

static error correction means connected to said computer means and tosaid first rebalance means to receive signals indicative of functions ofPs and M therefrom and operable to produce an output which varies inaccordance with AP;

and means connecting said static error correction means to said firstmember and to said second member to provide forces which vary inaccordance with AP thereto.

4. In a computer for a craft having a source of indicated staticpressure PS1 and a source of total pressure PT thereon:

a first circuit having a first input connected tothe source of Ps1, asecond input and providing a first output signal indicative of truestatic pressure Ps and a second output signal indicative of log Ps;

a -second circuit having a first input connected to the source of Psi, asecond input connected to the source of PT, a third input and providingan output signal indicative of log (PT-Ps);

summing means having a first input connected to said first circuit toreceive the second output signal indicative of log PS, having a secondinput connected to said second circuit to receive the output signalindicative of log (PT-Ps) and providing an output signal indicative oflog (PT-Ps)-log Ps;

characterized means @having an input connected to said summing means toreceive the output signal indicative of log (PT-PS) log ls and providingan output indicative of PSY-Ps computing means having .a first inputconnected to said first circuit to receive the first output signalindicative of Ps, having a second input connected to said characterizedmeans to receive the ouput signal indicative of Psi-PS and providing anoutput signal indicative of Psi-Ps;

and means connecting the second input of said first circuit and thethird input of said second circuit to said computing means to receivethe output signal indicatve of PSV-$5.

5. An air data computer comprising in combination:

a first pressure transducer having an input signal indicative ofindicated static pressure Psi, having an input signal indicative ofstatic error correction AP and operable to combine the Ps, and AP inputsignals to produce an output signal which is a function of correctedstatic pressure Ps;

a second pressure transducer having an input signal indicative of Psi,having an input signal indicative of total pressure PT, having an inputsignal indicative of AP and operable to combine the Psi, PT and AP inputsignals to produce an output signal which is qc and is a functon of thedifference in pressure between corrected static pressure and totalpressure;

computer means connected to said first pressure transducer and saidsecond pressure transducer to receive signals which are functions of Psand qs and opera-ble to produce a signal which is a function of Machnumber M;

correction signal generating means connected to said first pressuretransducer and said computer means to receive signals which arefunctions of Ps and M and operable to produce a signal indicative of AP;

and means connecting said first pressure transducer and said secondpressure transducer to said correction signal generating means toprovide the signal indicative of AP to said first pressure transducerand said second pressure transducer.

6. Apparatus of the class described comprising, in

combination:

a first pressure transducer having a first input connected to a sourceof indicated static pressure Ps1, having a second input connected to asource of static error `correction signal AP, and operable to produce anoutput signal which varies in accordance with changes of correctedstatic pressure Ps;

a second pressure transducer having a first input connected to thesource of Ps1, having a second input connected to a source of totalpressure PT, having a third input connected to the source of AP andoperable to produce an output signal which varies in accordance withchanges of differential pressure (PT-PS);

computing means having a first input connected to said first pressuretransducer to receive a signal therefrom which is a function of Ps,having a second 'input connected to said second pressure transducer toreceive a signal therefrom which is a function of (PT-Ps) and operableto produce an output signal which is a function of Mach number M;

and means connecting said first pressure transducer and said computingmeans to the source of AP to provide inputs thereto which vary with Psand M.

7. An air data computer comprising in combination:

a source of indicated static pressure signal Ps1;

a source of total pressure signal PT;

a source of static error correction signal AP;

a first pressure transducer having a first input connected to saidsource of Psi, having a second input connected to said source of AP andproviding an output which is a function of corrected static pressure Ps;

a second pressure transducer having a first input connected to saidsource of Psi, having a second input connected to said source of PT,having a third input connected to said source of AP and providing anoutput which is a function of the pressure difference (PT-PS);

computer means connected to said first pressure transducer and to saidsecond pressure transducer to receive t-he outputs therefrom andoperable to produce an output which is a function of Mach number M;

and means connecting said source of AP to said cornputer means and tosaid first pressure transducer to receive signals indicative offunctions of M and of Ps therefrom and operable to produce thecorrection signal AP.

References Cited by the Examiner UNITED STATES PATENTS 2,621,855 12/1952Hauser 23S- 61 2,714,309 8/1955 Redemske 73--178 2,905,000 9/1959 Roth73-389 2,937,526 5/1960 Roche 73-389 3,006,193 10/1961 Li 73-4063,062,054 11/1962 Fitch 73-140 3,090,229 5/1963 Howard 73--182 3,094,8686/1963 Anderson et al. 73--178 3,132,244 5/1964 Kemmer et al 73-182 XLOUIS R. PRINCE, Primary Examiner.

LEO SMILOW, RICHARD C. QUEISSER, Examiners.

1. AIR DATA COMPUTING APPARATUS COMPRISING IN COMBINATION: FIRSTPRESSURE TRANSDUCING MEANS HAVING A FIRST INPUT CONNECTED TO A SOURCE OFINDICATED STATIC PRESSURE PSI, A SECOND INPUT CONNECTED TO A SOURCE OFPRESSURE CORRECTION SIGNAL $P AND AN OUTPUT PS; FIRST MOTIVE MEANSCONNECTED TO SAID FIRST PRESSURE TRANSDUCING MEANS AND OPERABLE BY THEOUTPUT THEREOF TO PRODUCE A MECHANICAL MOTION INDICATIVE OF LOG PS;FIRST REBALANCE MEANS INCLUDING MEANS CHARACTERIZED TO CONVERTMECHANICAL MOTION INDICATIVE OF LOG PS TO MECHANICAL MOTION INDICATIVEOF PS; MEANS CONNECTING SAID FIRST REBALANCE MEANS TO SAID FIRST MOTIVEMEANS AND TO SAID FIRST PRESSURE TRANSDUCING MEANS TO PROVIDE REBALANCEOF SAID FIRST PRESSURE TRANSDUCING MEANS; SECOND PRESSURE TRANSDUCINGMEANS HAVING A FIRST INPUT CONNECTED TO THE SOURCE OF PSI, HAVING ASECOND INPUT CONNECTED TO A SOURCE OF TOTAL PRESSURE PT, HAVING A THIRDINPUT CONNECTED TO THE SOURCE OF $P AND AN OUTPUT; SECOND MOTIVE MEANSCONNECTED TO SAID SECOND PRESSURE TRANSDUCING MEANS AND OPERABLE BY THEOUTPUT THEREOF TO PRODUCE A MECHANICAL MOTION INDICATIVE OF LOG QC;SECOND REBALANCE MEANS INCLUDING MEANS CHARACTERIZED TO CONVERTMECHANICAL MOTION INDICATIVE OF LOG QC TO MECHANICAL MOTION INDICATIVEOF QC; MEANS CONNECTING SAID SECOND REBALANCE MEANS TO SAID SECONDMOTIVE MEANS AND TO SAID SECOND PRESSURE TRANSDUCING MEANS TO PROVIDEREBALANCE OF SAID SECOND PRESSURE TRANSDUCING MEANS; MECHANICALDIFFERENCE MEANS CONNECTED TO SAID FIRST MOTIVE MEANS AND TO SAID SECONDMOTIVE MEANS AND OPERABLE TO PROVIDE A MECHANICAL OUTPUT MOTIONINDICATIVE OF THE DIFFERENCE BETWEEN LOG PS AND LOG QC; FURTHERCHARACTERIZED MEANS CONNECTED TO SAID MECHANICAL DIFFERENCE MEANS ANDOPERABLE TO CONVERT THE MECHANICAL OUTPUT MOTION THEREOF TO A SIGNALINDICATIVE OF MACH NUMBER M; MEANS CONNECTED TO SAID FURTHERCHARACTERIZED MEANS AND TO THE SOURCE OF $P SIGNAL TO PROVIDE A SIGNALINDICATIVE OF THE RATIO $P/PS TO THE SOURCE OF $P SIGNAL; AND MEANSCONNECTED TO SAID FIRST REBALANCE MEANS AND TO THE SOURCE OF $P SIGNALTO PROVIDE A SIGNAL INDICATIVE OF PS, SAID SOURCE OF $P SIGNAL OPERATINGTO MULTIPLY THE $P/PS, SIGNAL AND THE PS SIGNAL SO AS TO PRODUCE ASIGNAL INDICATIVE OF $P.